The engineer who deals with historic bridges becomes the focus of controversy in the course of determining the existing condition, predicting remaining useful life, and designing the repair or replacement. The owner must, with limited funds, protect the safety of the public by making sure the structures are up to code. The preservation community wants to retain them at any cost. Some bridges can be continued in use with load restrictions; others must be transported for lighter use elsewhere or else demolished. There are, however, various ways to strengthen historic bridges without destroying their appearance, and guidelines have been proposed by several agencies.